IL-2 binds three transmembrane receptor subunits: IL-2Rβ and IL-2Rγ, which together activate intracellular signaling events upon IL-2 binding, and CD25 (IL-2Rα) which serves to present IL-2 to the other 2 receptor subunits. The signals delivered by IL-2Rβγ include those of the PI3-kinase, Ras-MAP-kinase, and STAT5 pathways.
T cells require expression of CD25 to respond to the low concentrations of IL-2 that typically exist in tissues. T cells that express CD25 include both CD4+ FOXP3+ regulatory T cells (T-reg cells)—which are essential for suppressing autoimmune inflammation—and FOXP3− T cells that have been activated to express CD25. FOXP3− CD4+ T effector cells (T-eff) may be either CD4+ or CD8+ cells, both of which can be pro-inflammatory and may contribute to autoimmunity and other diseases where the subject's immune system attacks an organ or other tissues. IL-2-stimulated STAT5 signaling is crucial for normal T-reg cell growth and survival and for high FOXP3 expression.
Because of the low affinity IL-2 possesses for each of the three IL-2R chains, a further reduction in affinity for IL-2Rβ and IL-2Rγ could be offset by an increased affinity for CD25. Mutational variants of IL-2 have been generated. These IL-2 mutants can be referred to as IL-2 muteins and have been found useful in the treatment of various diseases. However, there is still a need for additional IL-2 muteins that can be used in various applications and compositions. The present embodiments satisfies these needs as well as others.